The Lymphatic System

 The lymphatic system consists of : 1. Lymphatic Vessels that carry lymph (clear watery liquid formed from tissue fluid) 2. Lymph tissue called lymph nodes.  Lymph nodes are often called glands.  The spleen, tonsils (lymph nodes in the throat) and thymus are also considered part of the Lymphatic System.

 The functions of the Lymphatic System are  Drainage – returns extra cellular (leaked) fluid to the blood  Transport – lipid (fats and oils) are absorbed from the small intestine and carried to the skin or other organs for storage.  Defence – filters blood. Germs that enter the blood or tissue fluid will pass through the lymph and lymph nodes, where WBC’s attack and destroy them. Swollen glands are actively fighting infection.

 When blood is pumped by the heart under high pressure, some plasma leaks out of the capillaries and into the space around the cells.  This extra-cellular fluid is collected by vessels called lymphatics.  The lymph moves along through the lymphatics by the action of our muscles.  Valves prevent the backflow of lymph in these vessels.  The direction of flow is controlled by valves in the lymph nodes (found in the groin, armpits etc).  These lymph nodes are also areas of lymphocyte action and can swell when the body is infected with a pathogen.  All lymph joins the blood stream in the Vena Cava just before entering the heart.

 Immunity is the ability of an organism to resist infection.  Pathogens are micro-organisms that can cause a disease.  Your have two types of defence system: General and Specific.  There are a number of types of immunity.  Natural, Acquired, Artificial and Passive.

 Skin provides a physical barrier  Mucus in our lungs trap germs  Cilia in our lungs remove the mucus  Acid in our stomach kill bacteria  Enzymes in our tears protect the eye  Platelets seal damaged blood vessels  White Blood Cells eat germs.

 Acquired immunity arises when an organism makes it own antibodies.  Antibodies are Y shaped proteins, which attach onto antigens (pathogens).  Each antibody is specific to one type of antigen.  Should an infection occur, lymphocytes rush to the area of infection and start producing antibodies.  It usually takes a couple of days for the right antibody to be produced that will match the invading antigen.

 Once a match is found, that lymphocyte is triggered to multiply.  This marks the cell for destruction by other white blood cells.  Some of these lymphocytes remain in the blood and act as memory cells.  Should the same antigen invade again, the body can react to the infection much more quickly. At this point, one is said to be immune from the disease.

 Some germs have the power to kill a human well before the correct antibody can be found.  For this reason, doctors have developed vaccination.  Vaccination involves injected “dead germs” which causes a particular disease into the bloodstream.  They cannot grow or cause major problems, but the body still detects them and produces antibodies against them.  Should the “real germ” invade, the body had the antibody ready to defend against it.

 Passive immunity involves the body using antibodies which were not produced in the body.  Examples include an unborn child receiving antibodies from the mother’s placenta and during breast feeding.